McGraw-Hill’s ARIS (Assessment Review and Instruction System) for General Chemistry

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GENERAL CHEMISTRY

RAYMOND

F

IFTH

E

DITION

The Essential Concepts

RAYMOND

F

IFTH

E

DITION

RAYMOND

F

IFTH

E

DITION

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A

BOUT THE

C

OVER

Molecules in the upper atmosphere are constantly being bombarded by high-energy particles from the sun. As a result, these molecules either break up into atoms and/or become ionized. Eventually, the electronically excited species return to the ground state with the emission of light, giving rise to the phenomenon called aurora borealis

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Raymond

CHANG

Williams College

G

ENERAL

C

HEMISTRY

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GENERAL CHEMISTRY: THE ESSENTIAL CONCEPTS, FIFTH EDITION

Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY 10020. Copyright © 2008 by The McGraw-Hill Companies, Inc. All rights reserved. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning.

Some ancillaries, including electronic and print components, may not be available to customers outside the United States.

This book is printed on acid-free paper.

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ISBN 978–0–07–304851–2 MHID 0–07–304851–8

ISBN 978–0–07–304857–4 (Annotated Instructor’s Edition) MHID 0–07–304857–7

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The credits section for this book begins on page C-1 and is considered an extension of the copyright page.

Library of Congress Cataloging-in-Publication Data

Chang, Raymond.

General chemistry : the essential concepts / Raymond Chang. – 5th ed. p. cm.

Includes index.

ISBN 978–0–07–304851–2 — ISBN 0–07–304851–8 (hard copy : alk. paper) 1. Chemistry–Textbooks. I. Title.

QD33.2.C48 2008

540–dc22 2006102621

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v

Raymond Chang

was born in Hong Kong and grew up in Shanghai and Hong

Kong, China. He received his B.Sc. degree in chemistry from London University, England, and his Ph.D. in chemistry from Yale University. After doing postdoctoral research at Washington University and teaching for a year at Hunter College of the City University of New York, he joined the chemistry department at Williams College, where he has taught since 1968.

Professor Chang has served on the American Chemical Society Examination Committee, the National Chemistry Olympiad Examination Committee, and the Graduate Record Examinations (GRE) Committee. He is an editor of The Chemical Educator. Professor Chang has written books on physical chemistry, industrial chem-istry, and physical science. He has also coauthored books on the Chinese language, children’s picture books, and a novel for young readers.

For relaxation, Professor Chang maintains a forest garden, plays tennis, and prac-tices the violin.

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vii

List of Animations xvii Preface xix

A Note to the Student xxvi

1

Introduction 1

2

Atoms, Molecules, and Ions 28

3

Stoichiometry 58

4

Reactions in Aqueous Solutions 94

5

Gases 132

6

Energy Relationships in Chemical Reactions 171

7

The Electronic Structure of Atoms 206

8

The Periodic Table 245

9

Chemical Bonding I: The Covalent Bond 279

10

Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals 312

11

Introduction to Organic Chemistry 355

12

Intermolecular Forces and Liquids and Solids 390

13

Physical Properties of Solutions 425

14

Chemical Kinetics 454

15

Chemical Equilibrium 496

16

Acids and Bases 529

17

Acid-Base Equilibria and Solubility Equilibria 574

18

Thermodynamics 610

19

Redox Reactions and Electrochemistry 642

20

The Chemistry of Coordination Compounds 684

21

Nuclear Chemistry 708

22

Organic Polymers—Synthetic and Natural 739

A

PPENDIX

1

Units for the Gas Constant A-1

A

PPENDIX

2

Selected Thermodynamic Data at 1 atm and 25⬚_{C A-2}

A

PPENDIX

3

Mathematical Operations A-6

A

PPENDIX

4

The Elements and the Derivation of Their Names and Symbols A-9

Glossary G-1

Answers to Even-Numbered Problems AP-1 Credits C-1

Index I-1

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ix LIST OFANIMATIONS xvii

PREFACE xix

A NOTE TO THESTUDENT xxvi

Introduction 1

1.1

The Study of Chemistry 2

1.2

The Scientiﬁc Method 2

1.3

Classiﬁcations of Matter 4

1.4

Physical and Chemical Properties of Matter 7

1.5

Measurement 8

1.6

Handling Numbers 13

1.7

Dimensional Analysis in Solving Problems 18

KEYEQUATIONS22

SUMMARY OFFACTS ANDCONCEPTS22 KEYWORDS22

QUESTIONS ANDPROBLEMS 23

Atoms, Molecules, and Ions 28

2.1

The Atomic Theory 29

2.2

The Structure of the Atom 30

2.3

Atomic Number, Mass Number, and Isotopes 35

2.4

The Periodic Table 36

2.5

Molecules and Ions 38

2.6

Chemical Formulas 39

2.7

Naming Compounds 43

2.8

Introduction to Organic Compounds 52

SUMMARY OFFACTS ANDCONCEPTS52 KEYWORDS53

Stoichiometry 58

3.1

Atomic Mass 59

3.2

Avogadro’s Number and the Molar Mass of an Element 60

3.3

Molecular Mass 64

3.4

The Mass Spectrometer 66

3.5

Percent Composition of Compounds 67

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4

5

C H A P T E R

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3.6

Experimental Determination of Empirical Formulas 70

3.7

Chemical Reactions and Chemical Equations 73

3.8

Amounts of Reactants and Products 77

3.9

Limiting Reagents 81

3.10

Reaction Yield 83

KEYEQUATIONS85

SUMMARY OFFACTS ANDCONCEPTS 85 KEYWORDS86

Reactions in Aqueous Solutions 94

4.1

General Properties of Aqueous Solutions 95

4.2

Precipitation Reactions 97

4.3

Acid-Base Reactions 101

4.4

Oxidation-Reduction Reactions 106

4.5

Concentration of Solutions 114

4.6

Solution Stoichiometry 118

KEYEQUATIONS123

Gases 132

5.1

Substances That Exist as Gases 133

5.2

Pressure of a Gas 134

5.3

The Gas Laws 136

5.4

The Ideal Gas Equation 142

5.5

Dalton’s Law of Partial Pressures 148

5.6

The Kinetic Molecular Theory of Gases 153

5.7

Deviation from Ideal Behavior 159

KEYEQUATIONS162

Energy Relationships in Chemical

Reactions 171

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Contents xi

6.6

Standard Enthalpy of Formation and Reaction 191

KEYEQUATIONS197

The Electronic Structure of Atoms 206

7.1

From Classical Physics to Quantum Theory 207

7.2

The Photoelectric Effect 211

7.3

Bohr’s Theory of the Hydrogen Atom 212

7.4

The Dual Nature of the Electron 217

7.5

Quantum Mechanics 219

7.6

Quantum Numbers 221

7.7

Atomic Orbitals 222

7.8

Electron Conﬁguration 226

7.9

The Building-Up Principle 233

KEYEQUATIONS237

The Periodic Table 245

8.1

Development of the Periodic Table 246

8.2

Periodic Classiﬁcation of the Elements 247

8.3

Periodic Variation in Physical Properties 250

8.4

Ionization Energy 256

8.5

Electron Afﬁnity 259

8.6

Variation in Chemical Properties of the Representative Elements 261

SUMMARY OFFACTS ANDCONCEPTS 272 KEYWORDS272

Chemical Bonding I: The

Covalent Bond 279

9.1

Lewis Dot Symbols 280

9.2

The Ionic Bond 281

9.3

Lattice Energy of Ionic Compounds 283

9.4

The Covalent Bond 285

9.5

Electronegativity 287

9.6

Writing Lewis Structures 291

9.7

Formal Charge and Lewis Structures 293

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xii Contents

9.8

The Concept of Resonance 296

9.9

Exceptions to the Octet Rule 298

9.10

Bond Enthalpy 302

KEYEQUATION 305

Chemical Bonding II: Molecular

Geometry and Hybridization of

Atomic Orbitals 312

10.1

Molecular Geometry 313

10.2

Dipole Moments 322

10.3

Valence Bond Theory 325

10.4

Hybridization of Atomic Orbitals 328

10.5

Hybridization in Molecules Containing Double and Triple Bonds 337

10.6

Molecular Orbital Theory 340

KEYEQUATIONS348

Introduction to Organic

Chemistry 355

11.1

Classes of Organic Compounds 356

11.2

Aliphatic Hydrocarbons 356

11.3

Aromatic Hydrocarbons 370

11.4

Chemistry of the Functional Groups 374

11.5

Chirality—The Handedness of Molecules 381

SUMMARY OFFACTS ANDCONCEPTS384 KEYWORDS384

Intermolecular Forces and

Liquids and Solids 390

12.1

The Kinetic Molecular Theory of Liquids and Solids 391

12.2

Intermolecular Forces 392

12.3

Properties of Liquids 398

12.4

Crystal Structure 401

12.5

Bonding in Solids 405

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Contents xiii

12.6

Phase Changes 408

12.7

Phase Diagrams 415

KEYEQUATIONS417

Physical Properties

of Solutions 425

13.1

Types of Solutions 426

13.2

A Molecular View of the Solution Process 426

13.3

Concentration Units 429

13.4

Effect of Temperature on Solubility 432

13.5

Effect of Pressure on the Solubility

of Gases 433

13.6

Colligative Properties 435

KEYEQUATIONS447

Chemical Kinetics 454

14.1

The Rate of a Reaction 455

14.2

The Rate Laws 459

14.3

Relation Between Reactant Concentrations and Time 463

14.4

Activation Energy and Temperature Dependence of Rate Constants 471

14.5

Reaction Mechanisms 477

14.6

Catalysis 480

KEYEQUATIONS486

Chemical Equilibrium 496

15.1

The Concept of Equilibrium 497

15.2

Ways of Expressing Equilibrium Constants 500

15.3

What Does the Equilibrium Constant Tell Us? 507

15.4

Factors That Affect Chemical Equilibrium 512

KEYEQUATIONS519

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xiv Contents

Acids and Bases 529

16.1

Brønsted Acids and Bases 530

16.2

The Acid-Base Properties of Water 531

16.3

pH—A Measure of Acidity 533

16.4

Strength of Acids and Bases 536

16.5

Weak Acids and Acid Ionization

Constants 540

16.6

Weak Bases and Base Ionization Constants 551

16.7

The Relationship Between Conjugate Acid-Base Ionization Constants 553

16.8

Molecular Structure and the Strength of Acids 554

16.9

Acid-Base Properties of Salts 557

16.10

Acidic, Basic, and Amphoteric Oxides 563

16.11

Lewis Acids and Bases 565

KEYEQUATIONS567

Acid-Base Equilibria and

Solubility Equilibria 574

17.1

Homogeneous Versus Heterogeneous Solution Equilibria 575

17.2

Buffer Solutions 575

17.3

A Closer Look at Acid-Base Titrations 580

17.4

Acid-Base Indicators 586

17.5

Solubility Equilibria 589

17.6

The Common Ion Effect and Solubility 596

17.7

Complex Ion Equilibria and Solubility 597

17.8

Application of the Solubility Product Principle

to Qualitative Analysis 600

KEYEQUATIONS603

Thermodynamics 610

18.1

The Three Laws of Thermodynamics 611

18.2

Spontaneous Processes 611

18.3

Entropy 612

18.4

The Second Law of Thermodynamics 617

17

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Contents xv

18.5

Gibbs Free Energy 622

18.6

Free Energy and Chemical Equilibrium 629

18.7

Thermodynamics in Living Systems 632

KEYEQUATIONS634

Redox Reactions and

Electrochemistry 642

19.1

Redox Reactions 643

19.2

Galvanic Cells 646

19.3

Standard Reduction Potentials 648

19.4

Spontaneity of Redox Reactions 654

19.5

The Effect of Concentration on Cell Emf 657

19.6

Batteries 661

19.7

Corrosion 665

19.8

Electrolysis 668

19.9

Electrometallurgy 673

KEYEQUATIONS674

The Chemistry of Coordination

Compounds 684

20.1

Properties of the Transition Metals 685

20.2

Coordination Compounds 688

20.3

Geometry of Coordination Compounds 693

20.4

Bonding in Coordination Compounds:

Crystal Field Theory 695

20.5

Reactions of Coordination Compounds 701

20.6

Coordination Compounds in Living Systems 702

KEYEQUATION 703

19

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xvi Contents

Nuclear Chemistry 708

21.1

The Nature of Nuclear Reactions 709

21.2

Nuclear Stability 711

21.3

Natural Radioactivity 716

21.4

Nuclear Transmutation 720

21.5

Nuclear Fission 722

21.6

Nuclear Fusion 727

21.7

Uses of Isotopes 729

21.8

Biological Effects of Radiation 732

KEYEQUATIONS733

Organic Polymers—Synthetic

and Natural 739

22.1

Properties of Polymers 740

22.2

Synthetic Organic Polymers 740

22.3

Proteins 744

22.4

Nucleic Acids 752

SUMMARY OFFACTS ANDCONCEPTS 754 KEYWORDS755

A

PPENDIX

1

Units for the Gas Constant A-1

A

PPENDIX

2

Selected Thermodynamic Data at

1 atm and 25

⬚

C A-2

A

PPENDIX

3

Mathematical Operations A-6

A

PPENDIX

4

The Elements and the Derivation of

Their Names and Symbols A-9

GLOSSARY G-1

ANSWERS TOEVEN-NUMBEREDPROBLEMS AP-1

CREDITS C-1

INDEX I-1

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C H A P T E R

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xvii

The animations below are correlated to

General Chemistry within each chapter in two ways. The first is the Interactive Activity Summary found in the opening pages of every chapter. Then within the chapter are icons inform-ing the student and instructor that an animation is avail-able for a specific topic and where to find the animation for viewing on our Chang General ChemistryARIS web-site. For the instructor, the animations are also available on the Chemistry Animations Library DVD.

Chang Animations

Absorption of color (20.4) Acid-base titrations (17.3) Acid ionization (16.5) Activation energy (14.4)

Alpha, beta, and gamma rays (2.2) Alpha-particle scattering (2.2) Atomic and ionic radius (8.3) Base ionization (16.6) Buffer solutions (17.2) Catalysis (14.6) Cathode ray tube (2.2) Chemical equilibrium (15.1) Chirality (11.5)

Collecting a gas over water (5.5) Diffusion of gases (5.6)

Dissolution of an ionic and a covalent compound (13.2) Electron conﬁgurations (7.8)

Emission spectra (7.3)

Equilibrium vapor pressure (12.6) Formal charge calculations (9.5) Galvanic cells (19.2)

Gas laws (5.3) Heat ﬂow (6.4) Hybridization (10.4) Hydration (4.1)

Ionic vs. covalent bonding (9.4) Le Châtelier’s principle (15.4) Limiting reagent (3.9) Making a solution (4.5) Millikan oil drop (2.2) Neutralization reactions (4.3) Nuclear ﬁssion (21.5) Orientation of collision (14.4) Osmosis (13.6)

Oxidation-reduction reactions (4.4 & 19.1) Packing spheres (12.4)

Polarity of molecules (10.2) Precipitation reactions (4.2)

Preparing a solution by dilution (4.5) Radioactive decay (21.3)

Resonance (9.8)

Sigma and pi bonds (10.5)

Strong electrolytes, weak electrolytes, and nonelectrolytes (4.1)

VSEPR (10.1)

McGraw-Hill Animations

Atomic line spectra (7.3) Charles’ law (5.3)

Cubic unit cells and their origins (12.4) Dissociation of strong and weak acids (16.5) Dissolving table salt (4.1)

Electronegativity (9.5) Equilibrium (15.1)

Exothermic and endothermic reactions (6.2) Formal Charge Calculations (9.7)

Formation of an ionic compound (9.3) Formation of the covalent bond in H2 (10.4) Half-life (14.3)

Inﬂuence of shape on polarity (10.2) Law of conservation of mass (2.1)

Molecular shape and orbital hybridization (10.4) Nuclear medicine (21.7)

Operation of voltaic cell (19.2)

Oxidation-reduction reaction (4.4 & 19.1) Phase diagrams and the states of matter (12.7) Reaction rate and the nature of collisions (14.4) Three states of matter (1.3)

Using a buffer (17.2)

VSEPR theory and the shapes of molecules (10.1)

Simulations

Stoichiometry (Chapter 3) Ideal gas law (Chapter 5) Kinetics (Chapter 14) Equilibrium (Chapter 15) Titration (Chapter 17) Electrochemistry (Chapter 19) Nuclear (Chapter 21)

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xix

In this ﬁfth edition of General Chemistry: The Essential Concepts, I have continued the tradition of presenting only the material that is essential to a one-year general chemistry course. As with previous editions, I have included all the core topics that are necessary for a solid foundation in general chemistry without sacriﬁcing depth, clarity, or rigor.

General Chemistry covers these topics in the same depth and at the same level as 1100-page texts. Therefore, this book is not a condensed version of a big text. I have written it so that an instructor can cover 95 percent of the content, instead of the two-thirds or three-quarters that in my experience is typical of the big books. My hope is that this concise-but-thorough approach will appeal to efﬁciency-minded instructors and will please value-conscious students. The responses I have received from users over the years convince me that there is a strong need for such a text.

What’s New in This Edition?

Many sections have been revised and updated based on the comments from reviewers and users. Some examples are:

• An introduction to organic compounds has been added to Section 2.8.

• Ionic bonding has been added to Section 9.2. • Section 14.3 now also discusses zero-order reactions

in addition to ﬁrst- and second-order reactions. • Section 16.3 compares the deﬁnition of pH using

concentration and activity.

• Many new problems have been added under the Special Problems section in each chapter.

• The ARIS electronic homework system is available for the ﬁfth edition. ARIS will enhance the student learning experience, administer assignments, track student progress, and administer an instructor’s course. The students can locate the animations and interactives noted in the text margins in ARIS. Quizzing and homework assigned by the instructor is available in the ARIS electronic homework program.

Art

As always, I strive for a clean but visual design. For example, the following diagram shows the conversion of molecular hydrogen chloride to hydrochloric acid.

I have also added new molecular art to line drawings and photos and to a number of end-of-chapter problems. In addition, we have updated the photo program to complement the visual layout of the design. Finally, we have updated the format of the periodic table throughout the text.

All key equations and answers to many Worked Examples have been shaded for easy visual access. The key equations are also listed at the end of each chapter.

Problems

The development of problem-solving skills has always been a major objective of this text. For example, in Section 3.8 the general approach for solving stoichiom-etry problems is broken down in a numbered step-by-step process. Immediately following is Example 3.13 using this approach. Example 3.14 then requires the students to use this same type of process on their own.

(10.2) bond order⫽1

2a

number of electrons in bonding MOs ⫺

number of electrons in antibonding MOsb

Cl–

HCl

H3O+

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SolutionWe proceed as follows.

Step 1:The major species in solution are HCOOH, H⫹_{, and the conjugate base HCOO}⫺_.

Step 2:First we need to calculate the hydrogen ion concentration from the pH value

Taking the antilog of both sides, we get

Next we summarize the changes:

HCOOH(aq) H⫹₍_aq₎ _⫹ _HCOO⫺₍_aq₎

Initial (M): 0.10 0.00 0.00

Change (M): Equilibrium (M):

Note that because the pH and hence the H⫹_{ion concentration is known, it}

follows that we also know the concentrations of HCOOH and HCOO⫺_at

equilibrium.

Step 3:The ionization constant of formic acid is given by

CheckThe Kavalue differs slightly from the one listed in Table 16.3 because of the

rounding-off procedure we used in the calculation.

Practice ExerciseThe pH of a 0.060 Mweak monoprotic acid is 3.44. Calculate the

Kaof the acid.

⫽1.8⫻10⫺4 ⫽(4.1⫻10

⫺3_)(4.1 ⫻10⫺3₎

(0.10⫺4.1⫻10⫺3₎

Ka⫽

[H⫹_][HCOO⫺_]

[HCOOH]

4.1⫻10⫺3

(0.10⫺4.1⫻10⫺3₎

⫹4.1⫻10⫺3 ⫹4.1⫻10⫺3

⫺4.1⫻10⫺3 ∆

[H⫹_]_⫽₁₀⫺2.39

⫽4.1⫻10⫺3_M

2.39⫽ ⫺log[H⫹_]

pH⫽ ⫺log[H⫹_]

Marginal references enable students to apply new skills to other, similar problems at the end of the chapter. Each Worked Example is followed by a Practice Exercise that asks the students to solve a similar problem on their own. The answers to the Practice Exercises are provided after the end-of-chapter problems in each chapter.

xx Preface

Example 16.9

The pH of a 0.10 Msolution of formic acid (HCOOH) is 2.39. What is the Kaof the acid? StrategyFormic acid is a weak acid. It only partially ionizes in water. Note that the concentration of formic acid refers to the initial concentration, before ionization has started. The pH of the solution, on the other hand, refers to the equilibrium state. To calculate Ka, then, we need to know the concentrations of all three species: [H ],

[HCOO ], and [HCOOH] at equilibrium. As usual, we ignore the ionization of water. The following sketch summarizes the situation.

(C ti d)

As an instructor, I often tell my students that a good learning tool is to sketch out the inner workings of a problem. In some of the Worked Examples, I have included this type of drawing (for example, see Example 16.9 on p. 545). It is what a scientist would do as he or she works out a problem.

Step 2:To convert grams of C6H12O6to moles of C6H12O6, we write

Step 3:From the mole ratio, we see that 1 mol C6H12O6∞6 mol CO2. Therefore, the

number of moles of CO2formed is

Step 4:Finally, the number of grams of CO2formed is given by

After some practice, we can combine the conversion steps

into one equation:

CheckDoes the answer seem reasonable? Should the mass of CO2produced be larger

than the mass of C6H12O6reacted, even though the molar mass of CO2is considerably

less than the molar mass of C6H12O6? What is the mole ratio between CO2and

C6H12O6?

Practice ExerciseMethanol (CH3OH) burns in air according to the equation

If 209 g of methanol are used up in a combustion process, what is the mass of H2O

produced?

2CH3OH⫹3O2¡2CO2⫹4H2O ⫽1.25⫻103_{g CO}

2

mass of CO2⫽856 g C6H12O6⫻

1 mol C6H12O6

180.2 g C6H12O6⫻

6 mol CO2

1 mol C6H12O6⫻

44.01 g CO2

1 mol CO2

grams of C6H12O6¡moles of C6H12O6¡moles of CO2¡grams of CO2

28.50 mol CO2⫻44.01 g CO_{1 mol CO}2 2 ⫽

1.25⫻103_{g CO} 2

4.750 mol C6H12O6⫻

6 mol CO2

1 mol C6H12O6⫽

28.50 mol CO2

856 g C6H12O6⫻

1 mol C6H12O6

180.2 g C6H12O6⫽

4.750 mol C6H12O6

The food we eat is degraded, or broken down, in our bodies to provide energy for growth and function. A general overall equation for this very complex process repre-sents the degradation of glucose (C6H12O6) to carbon dioxide (CO2) and water (H2O):

If 856 g of C6H12O6is consumed by a person over a certain period, what is the mass

of CO2produced?

StrategyLooking at the balanced equation, how do we compare the amount of C6H12O6and CO2? We can compare them based on the mole ratiofrom the balanced

equation. Starting with grams of C6H12O6, how do we convert to moles of C6H12O6?

Once moles of CO2are determined using the mole ratio from the balanced equation

how do we convert to grams of CO2?

SolutionWe follow the preceding steps and Figure 3.8.

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Preface xxi

Pedagogy

The Interactive Activity Summary shows the avail-able media to further enhance students’ ability to understand a concept.

The Essential Conceptsin each chapter opener summarizes the main topics to be discussed in the chapter.

Marginal notes provide additional informa-tion to students regarding quick facts, referring students to a section in which the concept will be further detailed or linking back to a section they can use to review the material.

There is a plethora of molecular art in the margin, enabling students to “see” the molecule under discussion.

The periodic table icon in the margin illus-trates the properties of elements according to their positions in the periodic table.

Also in the margin, students will ﬁnd the icon highlighting the media (animations and interac-tives) that can be used to understand the concept presented.

The end of the chapter provides further study aids with the Key Equations, Summary of Facts and Concepts, and also the Key Words. They give students a quick snapshot of the chapter in review.

Molecular models are used to study complex biochemical reactions such as those between protein and DNA molecules.

C H A P T E R

Chemical Bonding II: Molecular Geometry and Hybridization of Atomic Orbitals

ESSENTIALCONCEPTS

Molecular GeometryMolecular geometry refers to the three-dimensional arrangement of atoms in a molecule. For relatively small molecules, in which the central atom contains two to six bonds, geometries can be reliably predicted by the valence-shell electron-pair repulsion (VSEPR) model. This model is based on the assumption that chemical bonds and lone pairs tend to remain as far apart as possible to minimize repulsion.

Dipole MomentsIn a diatomic molecule the difference in the electronegativities of bonding atoms results in a polar bond and a dipole moment. The dipole moment of a molecule made up of three or more atoms depends on both the polarity of the bonds and molecular geometry. Dipole moment measurements can help us distinguish between different possible geometries of a molecule.

Hybridization of Atomic OrbitalsHybridization is the quantum mechanical description of chemical bonding. Atomic orbitals are hybridized, or mixed, to form hybrid orbitals. These orbitals then interact with other atomic orbitals to form chemical bonds. Various molecular geometries can be generated by different hybridizations. The hybridization concept accounts for the excep-tion to the octet rule and also explains the formaexcep-tion of double and triple bonds.

Molecular Orbital TheoryMolecular orbital theory describes bonding in terms of the combination of atomic orbitals to form orbitals that are associated with the molecule as a whole. Molecules are stable if the number of electrons in bonding molecular orbitals is greater than that in antibonding molecular orbitals. We write electron conﬁgurations for molecular orbitals as we do for atomic orbitals, using the Pauli exclusion principle and Hund’s rule.

Activity Summary 1. Animation: VSEPR (10.1)

2. Interactivity: Determining Molecular Shape (10.1) 3. Animation: Polarity of Molecules (10.2) 4. Interactivity: Molecular Polarity (10.2) 5. Animation: Hybridization (10.4)

6. Interactivity: Determining Orbital Hybridization (10.4) 7. Animation: Sigma and Pi Bonds (10.5) 8. Interactivity: Energy Levels of Bonding—

Homonuclear Diatomic Molecules (10.6)

CHAPTEROUTLINE

10.1 Molecular Geometry 313

Molecules in Which the Central Atom Has No Lone Pairs• Molecules in Which the Central Atom Has One or More Lone Pairs•Geometry of Molecules with More Than One Central Atom •Guidelines for Applying the VSEPR Model

10.2 Dipole Moments 322

10.3 Valence Bond Theory 325

10.4 Hybridization of Atomic Orbitals 328

sp3_{Hybridization}_•_sp_{Hybridization}_•_sp2_{Hybridization}_•

Procedure for Hybridizing Atomic Orbitals•Hybridization ofs, p, and dOrbitals

10.5 Hybridization in Molecules Containing Double and Triple Bonds 331

10.6 Molecular Orbital Theory 340

Bonding and Antibonding Molecular Orbitals •Molecular Orbital Configurations

in which CH3COO is called the acetate ion. (In this book we will use the term disso-ciationfor ionic compounds and ionizationfor acids and bases.) By writing the formula of acetic acid as CH3COOH we indicate that the ionizable proton is in the COOH group. The double arrow 34in an equation means that the reaction is reversible;that is, the reaction can occur in both directions.Initially, a number of CH3COOH

mol-ecules break up to yield CH3COO and H ions. As time goes on, some of the

CH3COO and Hions recombine to form CH3COOH molecules. Eventually, a state is reached in which the acid molecules break up as fast as the ions recombine. Such a chemical state, in which no net change can be observed(although continuous activ-ity is taking place on the molecular level), is called chemical equilibrium.Acetic acid, then, is a weak electrolyte because its ionization in water is incomplete. By contrast, in a hydrochloric acid solution, the H and Cl ions have no tendency to recombine to form molecular HCl. We use the single arrow to represent complete ionizations.

In Sections 4.2– 4.4 we will study three types of reactions in the aqueous medium (precipitation, acid-base, and oxidation-reduction) that are of great importance to industrial, environmental, and biological processes. They also play a role in our daily experience.

4.2Precipitation Reactions

One common type of reaction that occurs in aqueous solution is the precipitation reaction,which results in the formation of an insoluble product, or precipitate.A

precipitateis an insoluble solid that separates from the solution.Precipitation reac-tions usually involve ionic compounds. For example, when an aqueous solution of lead(II) nitrate [Pb(NO3)2] is added to an aqueous solution of potassium iodide (KI),

a yellow precipitate of lead iodide (PbI2) is formed:

Potassium nitrate remains in solution. Figure 4.3 shows this reaction in progress. The preceding reaction is an example of a metathesis reaction(also called a dou-ble displacement reaction), a reaction that involves the exchange of parts between two

Pb(NO3)2(aq) 2KI(aq) ° PbI2(s) 2KNO3(aq)

4.2 Precipitation Reactions 97

There are different types of chemical equilibrium. We will return to this very important topic in Chapter 15.

Animation:

Precipitation Reactions ARIS, Animations

Figure 4.3

Formation of yellow PbI2precipitate as a solution of Pb(NO3)2is added to a solution of KI. K I Pb2 NO3 NO3 K I Pb2 88n

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xxii Preface

Interactives

Two sets of interactives are available with General Chemistry. The interactives enable students to manipu-late several variables. Students can “see” how changes affect the topic being studied. The seven topics include stoichiometry, the gas laws, kinetics, equilibrium, acid/base reactions, nuclear reactions and radioactivity, and the electrochemical cell. The other set of interactives are simple and fun learning tools that encompass a broad range of topics. All of these interactives are marked by the Interactive Activity icon.

Instructor Resources

Annotated Instructor’s Edition

By Raymond Chang. The Annotated Instructor’s Edition includes all resources available to instructors marked by icons located in the margins of the text. Information is

Media

The Interactive Activity Summary in the chapter opening pages enables students and instructors to see at a glance the media that can be incorporated into the learn-ing process. Within the text, an icon shows students where the concept in the animation or interactive is introduced. The icon directs students to the ARIS website for viewing. For instructors, there are also directions for ﬁnding the animation or interactive in the instructor materials.

Animations

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Preface xxiii

provided with regard to the integration of media (anima-tions, interactives, ARIS) and instructions as to where the instructor will ﬁnd the various media. The difﬁculty level of the end-of-chapter problems and the various chemical disciplines to which the problems are related to is indi-cated. Information on quality demonstration videos, tips for instructors, and the icons marking the digital assets available on the ARIS Presentation Center are provided.

ARIS

McGraw-Hill’s ARIS—Assessment, Review, and In-struction System—for General Chemistry is a complete electronic homework and course management system. Instructors can create and share course materials and assignments with colleagues with a few clicks of the mouse. Instructors can edit questions and algorithms,

import their own content, and create announcements and due dates for assignments. ARIS has automatic grading and reporting of easy-to-assign algorithmically generated homework, quizzing, and testing. Once a student is regis-tered in the course, all student activity within McGraw-Hill’s ARIS is automatically recorded and available to the instructor through a fully integrated grade book that can be downloaded to Excel.®

Go to www.aris.mhhe.com to learn more, or go directly to General ChemistryARIS site at www.mhhe.com/chang.

Presentation Center

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enhanced tests and quizzes, compelling course websites, or attractive printed support materials. The McGraw-Hill Presentation Center library includes thousands of assets from many McGraw-Hill titles. This ever-growing resource gives instructors the power to utilize assets speciﬁc to an adopted textbook as well as content from all other books in the library. The Presentation Center can be accessed from the instructor side of your textbook’s ARIS website, and the Presentation Center’s dynamic search engine allows you to explore by discipline, course, textbook chapter, asset type, or keyword. Simply browse, select, and download the ﬁles you need to build engaging course materials. All assets are copyright McGraw-Hill Higher Education but can be used by instructors for classroom purposes.

Instructor’s Testing and Resource

CD-ROM

The Test Bankis written by John Adams (University of Missouri) and the Instructor’s Solution Manual by Brandon J. Cruickshank (Northern Arizona University) and Raymond Chang. The Test Bank contains over 2000 multiple choice and short-answer questions. The ques-tions, which are graded in difﬁculty, are comparable to the problems in the text. The Test Bank is formatted for integration into the following course management systems: WebCT and Blackboard.

The Instructor’s Testing and Resource CD-ROM also contains the electronic ﬁle of the Instructor’s Solution Manual. The solutions to all of the end-of-chapter problems are given in the manual. This manual is included on the Instructor’s Testing and Resource CD-ROM.

Overhead Transparencies

Approximately 260 full-color text illustrations are repro-duced on acetate for overhead projection.

eInstruction

McGraw-Hill has partnered with eInstruction to provide the RF (radio frequency) Classroom Performance System(CPS), to bring interactivity into the classroom. CPS is a wireless response system that gives the instruc-tor and students immediate feedback from the entire class. The wireless response pads are essentially remotes that are easy to use and engage students. CPS enables you to motivate student preparation, interactiv-ity, and active learning so you can receive immediate

feedback and know what students understand. A text-speciﬁc set of questions, formatted for PowerPoint, is available via download from the Instructor area of the ARIS textbook website.

Cooperative Chemistry

Laboratory Manual

By Melanie Cooper (Clemson University). This innova-tive guide features open-ended problems designed to simulate experience in a research lab. Working in groups, students investigate one problem over a period of several weeks, so that they might complete three or four projects during the semester, rather than one preprogrammed experiment per class. The emphasis here is on experi-mental design, analysis problem solving, and communi-cation.

Student Resources

Problem-Solving Workbook

with Solutions

By Brandon J. Cruickshank (Northern Arizona University) and Raymond Chang is a success guide writ-ten for use with General Chemistry. It aims to help students hone their analytical and problem-solving skills by presenting detailed approaches to solving chemical problems. Solutions for all of the text’s even-numbered problems are included.

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ARIS

For students, ARIS contains the animations and interac-tivities listed in the Interactive Activity list at the begin-ning of each chapter. ARIS also features interactive quizzes for each chapter of the text. This program enables students to complete their homework online, as assigned by their instructors.

Chang Chemistry Resource Card

Our resource card is an easy, quick source of information on general chemistry. The student will ﬁnd the periodic table, basic tables, and key equations within reach with-out having to consult the text.

Schaum’s Outline of College Chemistry

By Jerome Rosenberg, Michigan State University, and Lawrence Epstein, University of Pittsburgh. This helpful study aid provides students with hundreds of solved and supplementary problems for the general chemistry course.

Acknowledgments

Reviewers

I would like to thank the following individuals who reviewed or participated in various McGraw-Hill symposia on general chemistry. Their insight into the needs of students and instructors were invaluable to me in preparing this revision:

Kathryn S. Asala University of Wisconsin–Whitewater

R. D. Braun University of Louisiana

Dana Chateilier University of Delaware

Beverly A. Clement Blinn College

Elzbieta Cook Louisiana State University

Nordulf W. G. Debye Towson University

Becky Gee Long Island University

Stephen Z. Goldberg Adelphi University

Robert Keil Moorpark College

Tracy Knowles Bluegrass Community and Technical College

Arthur A. Low Tarleton State University

Kristen L. Murphy University of Wisconsin–Milwaukee

Eric Potma University of California–Irvine

Bala Ramachandran Louisiana Tech University

James Schlegel Rutgers University

Mark W. Schraf West Virginia University

Lynn L. Thompson Butler County Community College

Paul J. Toscano State University of New York at Albany

Tim Zauche University of Wisconsin–Platteville

My thanks go to Michael Wood for his thorough review of the entire manuscript and his thoughtful comments.

As always, I have beneﬁted much from discussions with my colleagues at Williams College and correspon-dence with many instructors here and abroad.

It is a pleasure to acknowledge the support given to me by the following members of McGraw-Hill’s College Division: Doug Dinardo, Tammy Ben, Marty Lange, Kent Peterson, and Kurt Strand. In particular, I would like to mention Gloria Schiesl for supervising the produc-tion, David Hash for the book design, Daryl Bruﬂodt and Judi David for the media, and Todd Turner, the marketing manager, for his suggestions and encouragement. My publisher Thomas Timp and my editor Tami Hodge provided advice and support whenever I needed them. Finally, my special thanks go to Shirley Oberbroeckling, the developmental editor, for her care and enthusiasm for the project, and supervision at every stage of the writing of this edition

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xxvi

General chemistry is commonly perceived to be more difficult than most other subjects. There is some justifica-tion for this percepjustifica-tion. For one thing, chemistry has a very specialized vocabulary. At first, studying chemistry is like learning a new language. Furthermore, some of the concepts are abstract. Nevertheless, with diligence you can complete this course successfully, and you might even enjoy it. Here are some suggestions to help you form good study habits and master the material in this text.

• Attend classes regularly and take careful notes. • If possible, always review the topics discussed in

class the same day they are covered in class. Use this book to supplement your notes.

• Think critically. Ask yourself if you really under-stand the meaning of a term or the use of an equation. A good way to test your understanding is to explain a concept to a classmate or some other person. • Do not hesitate to ask your instructor or your

teach-ing assistant for help.

The fifth edition tools for General Chemistry are designed to enable you to do well in your general chem-istry course. The following guide explains how to take full advantage of the text, technology, and other tools.

• Before delving into the chapter, read the chapter

outlineand the chapter introductionto get a sense of the important topics. Use the outline to organize your notetaking in class.

• Use the Interactive Activity Iconas a guide to review challenging concepts in motion. The animations and interactives are valuable in presenting a concept and allowing the student to ma-nipulate or choose steps so full understanding can take place.

• At the end of each chapter you will ﬁnd a summary of facts and concepts, key equations, and a list of key words, all of which will help you review for exams.

• Deﬁnitions of the key words can be studied in con-text on the pages cited in the end-of-chapter list or in the glossary at the back of the book.

• ARIS houses an extraordinary amount of resources. Go to www.mhhe.com/physsci/chemistry/chang and click on the appropriate cover to explore chapter quizzes, animations, interactivities, simulations, and more.

• Careful study of the worked-out examples in the body of each chapter will improve your ability to an-alyze problems and correctly carry out the calcula-tions needed to solve them. Also take the time to work through the practice exercise that follows each example to be sure you understand how to solve the type of problem illustrated in the example. The an-swers to the practice exercises appear at the end of the chapter, following the homework problems. For additional practice, you can turn to similar home-work problems referred to in the margin next to the example.

• The questions and problems at the end of the chapter are organized by section.

• For even more practice problems, use ChemSkill Builder. ChemSkill Builder is a problem-solving tutorial with hundreds of problems that include feedback.

• The back inside cover shows a list of important ﬁg-ures and tables with page references. This index makes it convenient to quickly look up information when you are solving problems or studying related subjects in different chapters.

If you follow these suggestions and stay up-to-date with your assignments, you should ﬁnd that chemistry is challenging, but less difﬁcult and much more interesting than you expected.

Raymond Chang

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A hydrogen-filled balloon exploding when heated with a flame. The hydrogen gas reacts with oxygen in air to form water. Chemistry is the study of the properties of matter and the changes it undergoes.

Introduction

E

SSENTIAL

C

ONCEPTS

The Study of Chemistry Chemistry is the study of the properties of matter and the changes it undergoes. Elements and compounds are substances that take part in chemical transformation.

Physical and Chemical Properties To characterize a substance, we need to know its physical properties, which can be observed without changing its identity, and chemical properties, which can be demonstrated only by chemical changes.

Measurements and Units Chemistry is a quantitative science and requires measurements. The measured quantities (for exam-ple, mass, volume, density, and temperature) usually have units associated with them. The units used in chemistry are based on the international system (SI) of units.

Handling Numbers Scientific notation is used to express large and small numbers, and each number in a measurement must indicate the meaningful digits, called significant figures.

Doing Chemical Calculations A simple and effective way to perform chemical calculations is dimensional analysis. In this procedure, an equation is set up in such a way that all the units cancel except the ones for the ﬁnal answer.

Activity Summary

1. Interactivity: Substances and Mixtures (1.3) 2. Interactivity: Elements (1.3)

3. Interactivity: SI Base Units (1.5) 4. Interactivity: Unit Prefixes (1.5)

5. Interactivity: Density (1.5)

6. Interactivity: Accuracy and Precision (1.6) 7. Interactivity: Dimensional Analysis Method (1.7)

C

HAPTER

O

UTLINE

1.1 The Study of Chemistry 2

How to Study Chemistry

1.2 The Scientific Method 2

1.3 Classifications of Matter 4

Substances and Mixtures •Elements and Compounds

1.4 Physical and Chemical Properties of Matter 7

1.5 Measurement 8

SI Units •Mass and Weight •Volume •Density •

Temperature Scales

1.6 Handling Numbers 13

Scientific Notation •Significant Figures •Accuracy and Precision

1.7 Dimensional Analysis in Solving Problems 18

A Note on Problem Solving

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1.1

The Study of Chemistry

Whether or not this is your ﬁrst course in chemistry, you undoubtedly have some preconceived ideas about the nature of this science and about what chemists do. Most likely, you think chemistry is practiced in a laboratory by someone in a white coat who studies things in test tubes. This description is ﬁne, up to a point. Chem-istry is largely an experimental science, and a great deal of knowledge comes from laboratory research. In addition, however, today’s chemist may use a computer to study the microscopic structure and chemical properties of substances or employ sophisticated electronic equipment to analyze pollutants from auto emissions or toxic substances in the soil. Many frontiers in biology and medicine are currently being explored at the level of atoms and molecules—the structural units on which the study of chemistry is based. Chemists participate in the development of new drugs and in agricultural research. What’s more, they are seeking solutions to the problem of environmental pollution along with replacements for energy sources. And most industries, whatever their products, have a basis in chemistry. For exam-ple, chemists developed the polymers (very large molecules) that manufacturers use to make a wide variety of goods, including clothing, cooking utensils, artificial organs, and toys. Indeed, because of its diverse applications, chemistry is often called the “central science.”

How to Study Chemistry

Compared with other subjects, chemistry is commonly perceived to be more difficult, at least at the introductory level. There is some justification for this perception. For one thing, chemistry has a very specialized vocabulary. At first, studying chemistry is like learning a new language. Furthermore, some of the concepts are abstract. Nev-ertheless, with diligence you can complete this course successfully—and perhaps even pleasurably. Listed here are some suggestions to help you form good study habits and master the material:

• Attend classes regularly and take careful notes.

• If possible, always review the topics you learned in class the same day the top-ics are covered in class. Use this book to supplement your notes.

• Think critically. Ask yourself if you really understand the meaning of a term or the use of an equation. A good way to test your understanding is for you to explain a concept to a classmate or some other person.

• Do not hesitate to ask your instructor or your teaching assistant for help.

You will ﬁnd that chemistry is much more than numbers, formulas, and abstract the-ories. It is a logical discipline brimming with interesting ideas and applications.

1.2

The Scientific Method

All sciences, including the social sciences, employ variations of what is called the

scientific method—a systematic approach to research. For example, a psychologist who wants to know how noise affects people’s ability to learn chemistry and a chemist interested in measuring the heat given off when hydrogen gas burns in air follow roughly the same procedure in carrying out their investigations. The ﬁrst step is care-fully deﬁning the problem. The next step includes performing experiments, making careful observations, and recording information, or data, about the system—the part

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of the universe that is under investigation. (In these examples, the systems are the group of people the psychologist will study and a mixture of hydrogen and air.)

The data obtained in a research study may be both qualitative,consisting of gen-eral observations about the system, and quantitative, comprising numbers obtained by various measurements of the system.Chemists generally use standardized symbols and equations in recording their measurements and observations. This form of repre-sentation not only simpliﬁes the process of keeping records, but also provides a com-mon basis for communications with other chemists. Figure 1.1 summarizes the main steps of the research process.

When the experiments have been completed and the data have been recorded, the next step in the scientiﬁc method is interpretation, meaning that the scientist attempts to explain the observed phenomenon. Based on the data that were gathered, the researcher formulates a hypothesis,or tentative explanation for a set of observations.

Further experiments are devised to test the validity of the hypothesis in as many ways as possible, and the process begins anew.

After a large amount of data has been collected, it is often desirable to summa-rize the information in a concise way, as a law. In science, a lawis a concise verbal or mathematical statement of a relationship between phenomena that is always the same under the same conditions. For example, Sir Isaac Newton’s second law of motion, which you may remember from high school science, says that force equals mass times acceleration (F ⫽ _ma_{). What this law means is that an increase in the} mass or in the acceleration of an object always increases the object’s force propor-tionally, and a decrease in mass or acceleration always decreases the force.

Hypotheses that survive many experimental tests of their validity may evolve into theories. A theory is a unifying principle that explains a body of facts and/or those laws that are based on them.Theories, too, are constantly being tested. If a theory is disproved by experiment, then it must be discarded or modiﬁed so that it becomes consistent with experimental observations. Proving or disproving a theory can take years, even centuries, in part because the necessary technology is not available. Atomic theory, which we will study in Chapter 2, is a case in point. It took more than 2000 years to work out this fundamental principle of chemistry proposed by Democritus, an ancient Greek philosopher.

Scientiﬁc progress is seldom, if ever, made in a rigid, step-by-step fashion. Some-times a law precedes a theory; someSome-times it is the other way around. Two scientists may start working on a project with exactly the same objective, but may take drasti-cally different approaches. They may be led in vastly different directions. Scientists are, after all, human beings, and their modes of thinking and working are very much inﬂuenced by their backgrounds, training, and personalities.

The development of science has been irregular and sometimes even illogical. Great discoveries are usually the result of the cumulative contributions and experi-ence of many workers, even though the credit for formulating a theory or a law is usually given to only one individual. There is, of course, an element of luck involved in scientific discoveries, but it has been said that “chance favors the prepared mind.” It takes an alert and well-trained person to recognize the significance of an acciden-tal discovery and to take full advantage of it. More often than not, the public learns only of spectacular scientific breakthroughs. For every success story, however, there are hundreds of cases in which scientists spent years working on projects that ul-timately led to a dead end. Many positive achievements came only after many wrong turns and at such a slow pace that they went unheralded. Yet even the dead ends contribute something to the continually growing body of knowledge about the physical universe. It is the love of the search that keeps many scientists in the laboratory.

1.2 The Scientific Method 3

Representation Observation

Interpretation

Figure 1.1

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1.3

Classifications of Matter

Matteris anything that occupies space and has mass, and chemistryis the study of matter and the changes it undergoes.All matter, at least in principle, can exist in three states: solid, liquid, and gas. Solids are rigid objects with definite shapes. Liquids are less rigid than solids and are fluid—they are able to flow and assume the shape of their containers. Like liquids, gases are fluid, but unlike liquids, they can expand indefinitely.

The three states of matter can be interconverted without changing the composi-tion of the substance. Upon heating, a solid (for example, ice) will melt to form a liq-uid (water). (The temperature at which this transition occurs is called the melting point.) Further heating will convert the liquid into a gas. (This conversion takes place at the boiling point of the liquid.) On the other hand, cooling a gas will cause it to condense into a liquid. When the liquid is cooled further, it will freeze into the solid form. Figure 1.2 shows the three states of water. Note that the properties of water are unique among common substances in that the molecules in the liquid state are more closely packed than those in the solid state.

4 CHAPTER 1 Introduction

Figure 1.2

The three states of matter. A hot poker changes ice into water and steam.

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Substances and Mixtures

A substanceis matter that has a definite or constant composition and distinct prop-erties. Examples are water, silver, ethanol, table salt (sodium chloride), and carbon dioxide. Substances differ from one another in composition and can be identiﬁed by their appearance, smell, taste, and other properties. At present, over 20 million sub-stances are known, and the list is growing rapidly.

A mixture is a combination of two or more substances in which the substances retain their distinct identities.Some examples are air, soft drinks, milk, and cement. Mixtures do not have constant composition. Therefore, samples of air collected in dif-ferent cities would probably differ in composition because of differences in altitude, pollution, and so on.

Mixtures are either homogeneous or heterogeneous. When a spoonful of sugar dissolves in water, the composition of the mixture,after sufficient stirring, is the same throughout the solution. This solution is a homogeneous mixture. If sand is mixed with iron filings, however, the sand grains and the iron filings remain visible and sep-arate (Figure 1.3). This type of mixture, in which the composition is not uniform, is called a heterogeneous mixture.Adding oil to water creates another heterogeneous mixture because the liquid does not have a constant composition.

Any mixture, whether homogeneous or heterogeneous, can be created and then separated by physical means into pure components without changing the identities of the components. Thus, sugar can be recovered from a water solution by heating the solution and evaporating it to dryness. Condensing the water vapor will give us back the water component. To separate the iron-sand mixture, we can use a magnet to remove the iron ﬁlings from the sand, because sand is not attracted to the magnet (see Figure 1.3b). After separation, the components of the mixture will have the same com-position and properties as they did to start with.

Elements and Compounds

A substance can be either an element or a compound. An element is a substance that cannot be separated into simpler substances by chemical means.At present, 114 elements have been positively identiﬁed. (See the list inside the front cover of this book.)

1.3 Classifications of Matter 5

Interactivity:

Substances and Mixtures ARIS, Interactives

Interactivity:

Elements ARIS, Interactives

Figure 1.3

(a) The mixture contains iron filings and sand. (b) A magnet separates the iron filings from the mixture. The same technique is used on a larger scale to separate iron and steel from nonmagnetic objects such as aluminum, glass, and plastics.

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Chemists use alphabetical symbols to represent the names of the elements. The ﬁrst letter of the symbol for an element is alwayscapitalized, but the second letter is

nevercapitalized. For example, Co is the symbol for the element cobalt, whereas CO is the formula for carbon monoxide, which is made up of the elements carbon and oxygen. Table 1.1 shows some of the more common elements. The symbols for some elements are derived from their Latin names—for example, Au from aurum (gold), Fe from ferrum(iron), and Na from natrium (sodium)—although most of them are abbreviated forms of their English names.

Figure 1.4 shows the most abundant elements in Earth’s crust and in the human body. As you can see, only ﬁve elements (oxygen, silicon, aluminum, iron, and cal-cium) comprise over 90 percent of Earth’s crust. Of these ﬁve elements, only oxygen is among the most abundant elements in living systems.

Most elements can interact with one or more other elements to form compounds. We deﬁne a compoundas a substance composed of two or more elements chemically united in fixed proportions.Hydrogen gas, for example, burns in oxygen gas to form water, a compound whose properties are distinctly different from those of the start-ing materials. Water is made up of two parts of hydrogen and one part of oxygen. This composition does not change, regardless of whether the water comes from a faucet in the United States, the Yangtze River in China, or the ice caps on Mars. Unlike mixtures, compounds can be separated only by chemical means into their pure components.

Name Symbol Name Symbol Name Symbol

Aluminum Al Fluorine F Oxygen O

Arsenic As Gold Au Phosphorus P

Barium Ba Hydrogen H Platinum Pt

Bromine Br Iodine I Potassium K

Calcium Ca Iron Fe Silicon Si

Carbon C Lead Pb Silver Ag

Chlorine Cl Magnesium Mg Sodium Na

Chromium Cr Mercury Hg Sulfur S

Cobalt Co Nickel Ni Tin Sn

Copper Cu Nitrogen N Zinc Zn

TABLE 1.1 Some Common Elements and Their Symbols

Magnesium 2.8%

Oxygen

45.5% Oxygen

65%

Silicon

27.2% Carbon Hydrogen 10%

18% Calcium 4.7%

All others 5.3%

All others 1.2% Phosphorus 1.2% Calcium 1.6% Nitrogen 3% Iron 6.2%

Aluminum 8.3%

(a) (b)

Figure 1.4

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The relationships among elements, compounds, and other categories of matter are summarized in Figure 1.5.

1.4

Physical and Chemical Properties of Matter

Substances are identiﬁed by their properties as well as by their composition. Color, melting point, boiling point, and density are physical properties. A physical property can be measured and observed without changing the composition or identity of a sub-stance.For example, we can measure the melting point of ice by heating a block of ice and recording the temperature at which the ice is converted to water. Water dif-fers from ice only in appearance and not in composition, so this is a physical change; we can freeze the water to recover the original ice. Therefore, the melting point of a substance is a physical property. Similarly, when we say that helium gas is lighter than air, we are referring to a physical property.

On the other hand, the statement “Hydrogen gas burns in oxygen gas to form water” describes a chemical property of hydrogen because to observe this property we must carry out a chemical change,in this case burning. After the change, the orig-inal substances, hydrogen and oxygen gas, will have vanished and a chemically dif-ferent substance—water—will have taken their place. We cannot recover hydrogen and oxygen from water by a physical change such as boiling or freezing.

Every time we hard-boil an egg, we bring about a chemical change. When subjected to a temperature of about 100⬚_{C, the yolk and the egg white undergo reactions that alter}

not only their physical appearance but their chemical makeup as well. When eaten, the egg is changed again, by substances in the body called enzymes.This digestive action is another example of a chemical change. What happens during such a process depends on the chemical properties of the speciﬁc enzymes and of the food involved.

All measurable properties of matter fall into two categories: extensive properties and intensive properties. The measured value of an extensive property depends on how much matter is being considered.Mass, length, and volume are extensive prop-erties. More matter means more mass. Values of the same extensive property can be added together. For example, two copper pennies have a combined mass that is the sum of the masses of each penny, and the total volume occupied by the water in two beakers is the sum of the volumes of the water in each of the beakers.

1.4 Physical and Chemical Properties of Matter 7

Homogeneous mixtures

Mixtures

Separation by chemical methods Separation by

physical methods Matter

Pure substances

Heterogeneous

mixtures Compounds Elements

Figure 1.5

Classification of matter.

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The measured value of an intensive propertydoes not depend on the amount of mat-ter being considered. Temperature is an intensive property. Suppose that we have two beakers of water at the same temperature. If we combine them to make a single quan-tity of water in a larger beaker, the temperature of the larger amount of water will be the same as it was in two separate beakers. Unlike mass and volume, temperature and other intensive properties such as melting point, boiling point, and density are not additive.

1.5

Measurement

The study of chemistry depends heavily on measurement. For instance, chemists use measurements to compare the properties of different substances and to assess changes resulting from an experiment. A number of common devices enable us to make sim-ple measurements of a substance’s properties: The meterstick measures length; the buret, the pipet, the graduated cylinder, and the volumetric ﬂask measure volume (Figure 1.6); the balance measures mass; the thermometer measures temperature. These instruments provide measurements of macroscopic properties, which can be determined directly.Microscopic properties,on the atomic or molecular scale, must be determined by an indirect method,as we will see in Chapter 2.

A measured quantity is usually written as a number with an appropriate unit. To say that the distance between New York and San Francisco by car along a certain route is 5166 is meaningless. We must specify that the distance is 5166 kilometers. In science, units are essential to stating measurements correctly.

SI Units

For many years scientists recorded measurements in metric units, which are related decimally, that is, by powers of 10. In 1960, however, the General Conference of Weights and Measures, the international authority on units, proposed a revised metric

Graduated cylinder Volumetric flask Pipet

Buret

mL 100

90

80

70

60

50

40

30

20

10 mL

0

1

2

3

4

15

16

17

18

20 19

25 mL

1 liter Figure 1.6

Some common measuring devices found in a chemistry laboratory. These devices are not drawn to scale relative to one another. We will discuss the uses of these measuring devices in Chapter 4.

Interactivity:

SI Base Units ARIS, Interactives

Interactivity:

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system called the International System of Units (abbreviated SI, from the French

System International d’Unites). Table 1.2 shows the seven SI base units. All other SI units of measurement can be derived from these base units. Like metric units, SI units are modiﬁed in decimal fashion by a series of preﬁxes, as shown in Table 1.3. We use both metric and SI units in this book.

Measurements that we will utilize frequently in our study of chemistry include time, mass, volume, density, and temperature.

Mass and Weight

Mass is a measure of the quantity of matter in an object. The terms “mass” and “weight” are often used interchangeably, although, strictly speaking, they refer to dif-ferent quantities. In scientiﬁc terms, weight is the force that gravity exerts on an object. An apple that falls from a tree is pulled downward by Earth’s gravity. The mass of the apple is constant and does not depend on its location, but its weight does. For example, on the surface of the moon the apple would weigh only one-sixth what it does on Earth, because of the smaller mass of the moon. This is why astronauts

1.5 Measurement 9